Patent GB-855877-A (GB)
Title: Improvements in electric impulse producing systems
IPC: G06F1/10
Filed: 1957-03-20
Abstract: 855,877. Digital electric counting apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. March 20, 1957 [March 20, 1956], No. 9209/57. Class 106 (1). An impulse producing system comprises a plurality of chains of cascade-connected bi-stable triggers, a source of phase-displaced impulses for operating each chain of triggers, means interconnecting a trigger in one chain with a trigger in another chain, a source of control impulses and means responsive to a simultaneous occurrence of a control impulse and a phase-displaced impulse for rendering said chains of triggers alternately responsive to successively occurring ones of said phasedisplaced impulses. The device described, comprising two chains A and B of normally off triggers, along each of which a single on condition can be advanced, and in which stage-by-stage advancements of the two on conditions occur alternately in the two chains, is so arranged that the on condition in each chain can be caused to appear at any selected (by pre-plugging) stage, advance to a second selected stage, and then disappear, excepting that the on condition in the A chain always disappears immediately after that in the B chain, if it has not already disappeared. The device can also be controlled (by appropriate pre-plugging) so that when the on condition in the B chain reaches a selected stage, the on condition in the A chain skips from where it is directly to another selected stage. Each trigger, Fig. 1, is such that it requires a positive signal on terminal 4 together with a positive pulse on terminal 5 to alter its condition. A positive potential on terminal 4 passes through an inverter 6, and its effect is to lower the potential of the grid of triode 1, to a level which will not alter the state of the trigger even if triode 1 is conducting. A positive pulse applied at terminal 5 has its trailing edge differentiated to produce a negative pulse at the grid of triode 1. This, by itself, is also ineffective, but the combination of this negative pulse and a lowering of the grid potential is sufficient to cut-off triode 1, supposing it had been conducting which in turn causes the right-hand triode 1<SP>1</SP> to conduct, in which condition the trigger is said to be on. Thus a positive pulse on terminal 5 in the presence of a positive signal on terminal 4 turns the trigger from off to on, and similarly a positive pulse on terminal 51 in the presence of a positive signal on terminal 41 turns the trigger from on to off. A plurality of these triggers connected, basically, as shown in Fig. 2, form the two A and B chains. If stage (n+1), Fig. 2, is assumed to be on (right-hand side conducting) and the other two stages off, then a single positive pulse on lead 12 will turn on stage n (stage (n+1) remaining on), a single positive pulse on line 12<SP>1</SP> will turn off stage n, and simultaneous positive pulses on lines 12 and 121 will cause the on condition to advance from stage (n+1) to stage n. In the actual device, three stages of the A chain being shown arranged vertically on the right-hand side of Fig. 3b, and three stages of the B chain being shown on the left-hand side, the connection between the 11 terminal of one stage and the 4 terminal of the next stage, for example between stages (n+1) and n of the A chain, is via an " and " gate 18A, Fig. 3b, and a mixer 19n (or via a gate 18B and mixer 19n for the B chain), and the gates 18A and 18B are only enabled by a and b pulses, Fig. 4, a, b, on lines 16A and 16B, respectively, derived from a multivibrator 13, Fig. 3a, and the frequency halving circuits 14, 15. The two chains receive their advancing pulses, Fig. 4, e, f, on lines 12A, 12<SP>1</SP>A and lines 12B, 12<SP>1</SP>B, respectively. The two chains A and B are controlled by a programme chain C, Fig. 3a. Each stage of chain C has associated with it 5 hubs 20A, 21A, and 20B, 21B and 45<SP>1</SP> (only those hubs for stages M and (M - 1) being shown), the first four of which control the starting and stopping of the A chain, and the starting and stopping of the B chain, respectively, and the last of which is used when the chain A has to skip certain stages. The programme chain C is so arranged that when the programme associated with one stage has been completed (i.e. when chains A and B have advanced through the plugged ranges of stages) it advances to the next stage and the next programme is performed. To cause either the A or B chain to start at stage n, say, the appropriate 20 hub is connected to hub 26n, and to cause either the A or B chain to stop after stage m say, the appropriate 21 hub is connected to hub 26n - 1. When the programme chain advances a start trigger 24, Fig. 3a, is turned on (staying on for the period shown in Fig. 4, g) and the start terminals 20A and 20B produce two pulses, Figs. 4, i and j, respectively, which pulses are applied to the selected hubs 26, where they are effective to start the A and B chain. When chain B reaches the stage after which it must stop, say stage (n - 1), a stop signal passes through a gate 29n - 1 and a mixer 32, and a gate 37 and an inverter 41, thereby closing a gate 42 through which the B chain advance pulses normally pass. The next advancing pulse for chain B is therefore blocked and the on condition in chain B therefore disappears. This stop signal from mixer 32 also stops chain A (if not already stopped), by applying an extra pulse through a gate 43 to lead 12A, produces a new start signal by turning on start trigger 24, and advances the programme chain C, by pulsing its terminals 5, 5<SP>1</SP>. When it is desired that chain A shall skip from whereever it is to, say, stage n when chain B reaches, say, stage p, then hubs 45 and 45<SP>1</SP> are connected and hubs 46p and 26n are connected, in addition to the other start and stop connections made as described above.